It helps prevent all this kind of carry-on constantly...
As a kid I used to play games. I used to get home from school and play on Sonic the Hedgehog on the Sega Megadrive. I suppose it helped me to switch my brain off. They did not have tablets or mobile devices in those days I'm afraid!
Now I do have a mobile phone (hurray!) I have a Kindle and a laptop, but I just don't have any time for games. I know that some people play bingo games online but it's not something that I ever have the time for. The kids keep me very busy and when I am not studying or doing jobs in the house I am generally taking the kids out in the real world, getting fresh air and taking them out for new experiences.
I don't think that there is anything wrong specifically with letting the kids use tablets and mobile devices but I do think that like anything else, it should be in moderation. I like to monitor how much time they spend on them so that they do get a good balance in their lives.